Turbine blades are the primary elements of wind turbines for converting wind energy into electrical energy. The blades have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade. The lift force generates torque on the main rotor shaft, which is geared to a generator for producing electricity.
The turbine blades typically consist of a suction side shell and a pressure side shell that are bonded together at bond lines along the trailing and leading edges of the blade. The bond lines are generally formed by applying a suitable bonding paste or compound along the bond line with a minimum designed bond width between the shell members. These bonding lines are a critical design constraint of the blades. A significant number of turbine blade field failures are bond line related, particularly leading edge failures. Separation of the bond line along the leading edge of an operational turbine blade can result in a catastrophic failure and damage to the wind turbine.
In addition, the leading edge bonding process is a challenging and time consuming task. Application of the bond paste to achieve the required bonding thickness and width is difficult. Post-bond trimming of the leading edge to remove excess bond paste, trim reinforcement material, and so forth, is a time consuming and expensive finishing operation. Even after the trimming process, it is often necessary to perform subsequent edge repairs/modifications before the blade is field-ready. For example, if they occur, any leading edge “overbite” or “underbite” defects must be corrected. These overbite and underbite defects are the result of chord-wise misalignment between the upper and lower shell members.
Conventional leading edge bond configurations are also highly susceptible to erosion in the field, which results in costly and expensive field repairs.
U.S. Patent Application Pub. No. 2007/0036659 proposes a wind turbine blade construction wherein the shell components are joined at the leading and trailing edges and one or more front covers formed into a shape corresponding to the structure of the shell components are adhered to the shell components along the leading edge. This construction is alleged to reduce the “after-treatments” typically required after the shell components are joined, such as filling of the shell joints, scratches, cavities, and the like, with gel coat of other filler materials, as well as grinding and polishing of the leading edge.
U.S. Pat. No. 7,637,721 describes a trailing edge cap intended to be placed over the designed trailing edge of a wind turbine blade in order to reduce noise generated at the trailing edge. The cap has a configuration so as to extend well past the original trailing edge of the blade and to define a reduced trailing edge thickness as compared to the original trailing edge. The cap is flexible and is designed to conform to a variety of differently sized and shaped turbine blades. Although this trailing edge cap may provide reduced noise benefits, it does not address structural bonding issues associated with the trailing edge.
Accordingly, the industry would benefit from an improved bond configuration for a wind turbine blade that is cost effective, time efficient, and produces an improved structural bond, particularly along the leading edge of the wind turbine blade.